Induction furnace



Patented Sept. 9V, v1930 generally worked uNlTnn STATI-:s PATENT oFr-ic vmassiv FRANZ LINNHOFF, O l ELBERSWALDE, GERMANY, .ASSIGNOB TQAJA'X'. fTIi'ElYMIU A CORPORATION, QF TiiENTON, NEW JERSEY.

INDUCTION rUaNAcE Application led December 7, 1928, Serial No. 324,439, and in Germany Iarch 2, '1928.

This invention relates tol induction furnaces, more particularly to the type known as ironless induction furnaces having no iron core, although one portion of the magnetic path consists of iron. y

The electric ironless induction furnaces having been employed for melting or heating meta'ls and ores up'to the present time, are

with currents of high frequency and on that account are called high frequency furnaces. A furnace of thisv type consists essentially in a crucible being surrounded externally by an air or water cooled coil. For the production of the current of high frequencya converter unit is necessary comprising, f. i. a motor and a 4high frequency generator. If al lyphase motor is used, it may be connectedxto a `polyphas'e supply system. It has been found that it is economically advantageous to work such furnaces with currents of normal frequency (5G-60 cycles per second) It has also been proposed to work such furnaces with frequencies of 2 50=100 or 3X 50=150 cycles per second. Since with ironless induction crucibleffur` naces a converter unit is not required if the normal frequencyv i's used, 'the coil has been connected to one phase of a polyphase current supply. In this way the polyphase current installation is disadvanta eously loaded, which leads, particularly with the single phase connection of furnaces of large output, to increased losses in the installation. I

It is, therefore, an object of this invention to provide an ironless induction furnace adapted to be connected systematically to a polyphase supply system without increasing the loss of the installation.

Another object of this invention is to provide an ironless electric furnace making it possible to control the input of power according to the required power at any time.

he invention consists in subdividing the coil of the furnace and connecting'the parts together in a phase transformer circult of known type. It will be understood,`however, that instead of providing one subdivided coil the Crucible may be surrounded by two coils connected together in Scotts `method for changing three-phase into two-phase circuits.

.The invention will be readily understood lby reference to the accompanying drawing which represents dia-grammatically one'` embodiment of the invention.

rlhe Crucible l is surrounded by two coils '2 and 3 of copper two coils are connected toget er in Scotts system. Between the two coils 2 and 3 are the two rings 4 and 5 which-are made of transformer sheet iron. The iron rings are separated by an air space or a layer of a nonmagnetic material.

vThe field ofthe upper circuit is closed externally through the upper ring and the field of the lower circuit through the lower iron ring. The air space between these two iron rings is practically free from lines of force. Tie magnetic fieldsof the upper and lower circuit and of the currents flowing in the melting bath which are relatively displaced in Scotts circuit system by 90, are still more completely separated if the diameter of the lower part of the furnace is smaller than that -of the upper part. By this arrangement the magnetic screening action of the two iron rings is increased, since they exert a screening action both at right an les and also parallel to thecentral axis. lhe dia-meter of the iron rings may also be less than that of the lower coil, whereby the screening action of the iron rings is still further increased. This is, however, not'absolutely necessary; since the secondary currents only flow at t e periphery of the bath the fields produced are concentrated mainly at the periphery of the bath, near the iron rings and towards the centre of the bath are considerably reduced.

Between the crucible 1 and the coils 2 and 3 there are a heat insulating layer (3 and a strips or cop er tube. The

cylinder Y'l' of electric insulating material.

' 10 can be made of the same material.

` is below the pouring spout.-

The twolcoils areconnected 'to the polyphase current supply system by a three-pole switch 13. The lower coil can be wholly or partially connected by the switch 14, in order to adjust the power applied to the furnace. The upper coil can be included by closing the switch 15.

By tappings arranged within one or both coils the output can be controlled. For eX- ample, during the refining period in which less power is required, the upper coil can be cut olf by the switch 15, the lower coil alone remaining in circuit.- Phase compensation can be obtained, as in high frequency furnaces y by condensers if the conditions require it.

What is claimed is:

1. In a coreless induction furnace, in combination, a Crucible, two coils surrounding said crucible, a three-phase source' of alternat/ing current and a Scott connection whereby a two-phase Scott circuit may be applied to the coils.

2. In a coreless induction furnace, in combination, a Crucible and two coils surrounding said crucible, a three-phase source of current and a Scott connection whereby a two-phase Scott circuit may be connected'to the coils, the lower part of the furnace having a smaller each .coil from .magnetic interference from current in the other coil.

6. In a coreless induction furnace, a cruci ple, two inductor coils surrounding the crucie said indu'ctors and connections whereby the current can be passed through the lower coil or through both coils at will.

` In testimony whereof I affix my signature.

FRANZ LINNHOFF.

diameter than the upper' part, the two vcoils being applied about different furnace diameters.

3. In a coreless induction furnace, in combination, a Crucible, two coils surrounding said Crucible, rings of laminated magnetic material between the coils and a multiphase source of current for the coils whereby the sections surrounded by the two coils are subs stantially free each of induction from the other coil.

4. In a coreless induction furnace, in combination, av crucible, two-coils surrounding said Crucible, a source of current for the different coils, and rings of laminated iron laced betweensaid coils, the iron sheets bemg separated from one another 'by an air space. f

5. In a coreless induction furnace, a crucible having the diameter of its up er port-ion larger than that of the lowerportlon, two in-v ductor coils, one about each of the portions of the different diameters, a multi-phase source of current for the two 'coils and magnetic means between the coils for protecting a source of Scott connected current for 

